Solid ink or phase change ink printers conventionally receive ink in a solid form, either as pellets or as ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a melt plate in the heater assembly. The melt plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto an image receiving medium, such as an intermediate transfer surface. U.S. Pat. No. 5,734,402 for a Solid Ink Feed System, issued Mar. 31, 1998 to Rousseau et al.; U.S. Pat. No. 5,861,903 for an Ink Feed System, issued Jan. 19, 1999 to Crawford et al.; and U.S. Pat. No. 6,709,094 for a Load and Feed Apparatus for Solid Ink, issued Mar. 23, 2004 to Jones describe exemplary systems for delivering solid ink sticks into a phase change ink printer.
A color printer typically uses four colors of ink (yellow, cyan, magenta, and black). Ink sticks of each color are delivered through corresponding feed channels to a melt plate. The operator of the printer exercises care to avoid inserting ink sticks of one color into a feed channel for a different color. Ink sticks may be so saturated with color dye that it may be difficult for a printer user to tell by color alone which color is which. Cyan, magenta, and black ink sticks in particular can be difficult to distinguish visually based on color appearance. A key plate has keyed openings to aid the printer user in ensuring that only ink sticks of the proper color are inserted into each feed channel. Each keyed opening of the key plate has a unique shape. The ink sticks of the color for that feed channel have a shape corresponding to the shape of the keyed opening. The keyed openings and corresponding ink stick shapes exclude from each ink feed channel ink, sticks of all colors except the ink sticks of the proper color for that feed channel.
Ink sticks are generally cubic in volume and formed with one or more key elements. These key elements are protuberances or indentations that are located in different positions on an ink stick. In some cases, the key elements are placed on different sides of ink sticks of different colors that are included in an ink stick set. This allows for detection and identification of the different ink sticks, particularly during loading, as noted above. For instance, corresponding keys on the perimeters of the openings through which the ink sticks are inserted into their appropriate feed channel exclude ink sticks of the set, particularly those of different colors, which do not have the appropriate perimeter key element.
An ink stick is typically pushed or slid along the feed channel by the feed mechanism until it reaches the melt plate. However, the sticky nature of an ink stick's waxy exterior surface generates friction as the ink stick is pushed along the channel. This friction may cause stick-slip movement of the ink stick and the ink stick may hang up or catch within the feed channel. The friction encountered by an ink stick increases in proportion to the number of ink sticks that are in the feed channel. Problems also arise from an ink stick being incorrectly oriented within a correct feed channel. The misorientation of such an ink stick may be difficult for an operator to detect so the troublesome stick can be removed.
Some provisions have been made to prevent the solid masses of shaped ink from sticking to the sides of the feed chutes so that an unrestricted feed of ink sticks proceeds down the channel to the heater plate for melting. For instance, the feed channel and/or the ink stick may include cooperating alignment and orientation features that facilitate alignment of the generally rectangular cross-section ink sticks in the feed channel so the possibility of jamming due to skewing of the ink stick is reduced.
The areas on a typical ink stick for keying and guiding elements are typically small. Simply increasing the size of a stick to accommodate additional features is not beneficial because the lateral dimensions of the ink stick must not exceed the dimensions of the corresponding keyed opening or feed channel for the ink stick. While the small size allows improved resolution for topping off the ink supply when replenishing ink, an operator must supply a greater number of the ink sticks into the feed channel of the phase change ink printer, which increases the work load of the operator. As phase change ink printers have increased their printing speed, the smaller ink sticks must be replaced at an even greater rate.
Therefore, other methods for improving the efficiency of delivering solid ink sticks along the feed channel to the melt plate would be useful.